Electron microscopy of the uredinial and telial stages of the rust fungus, Puccinia imperatae

Abstract

The purpose of this work was to assess the morphology and ontogeny of Puccinia imperatae urediniospores and teliospores growing on its host, Imperata cylindrica, for the first time using scanning (SEM) and transmission (TEM) electron microscopy. The first evidence of uredinial development is the aggregation of hyphae in host intercellular spaces under the epidermis to form an uredinial initial. Uredinial primordia become evident as compact masses of fungal hyphae. The mycelia are dikaryotic and originated from dikaryotic urediniospores, which infect a new host. Dikaryotic sporogenous cells begin to form from dikaryotic mycelium as the uredinium develops further. The fundamental cell in the urediniospore and teliospore formation is the sporogenous cell. The teliospores with their persistent pedicels arise from dense dikaryotic sporogenous tissue, which later becomes highly vacuolated. The sporogenous cell forms a spore bud, which later divides into a pedicel and teliospore mother cell with two nuclei that produce the mature teliospore. SEM examination revealed that the urediniospores are echinulate bearing conical spines on their surfaces, sometimes curving near their tips, and the echinulate ornaments are distributed over the entire urediniospore surface. SEM examination also indicated that the teliospore surface shows rugose ornamentations. This investigation proved that the morphology of the uredinia of different Puccinia species is not related to the host species, but to the rust species. The possibility of using this fungus as a biological control agent for the noxious weed, Imperata cylindrica, was also discussed.